This disclosure relates to limb supports generally, to chair armrests specifically, and to ergonomic arm pads in particular. Horizontally movable arm pads are more preferable than stationary ones in part because they are adjustable to fit a user's desired supporting position. A horizontally movable armrest may be attached to an arm support through one or more slot tracks that permit the arm pad to move laterally. When independently actuable fasteners are inserted through the slot tracks to attach the arm pad to the arm support, the movement of the arm pad is bound by the edges of the slot tracks. In other words, the slot tracks guide the movement of the arm pad. As a user attempts to position the arm pad, such configurations can lead to misfunctioning, abrupt movement, or even an unintentionally locked arm pad because the fasteners are not cooperating and the fasteners knock along the edges of the slot tracks.